Modification to the Toroidal Rotation Velocity and Radial Electric Field by Pellet Injection in DIII-D

The ability to modify and control the radial electric field and its radial derivative can lead to direct control of radial transport of plasma in a toroidal device. In the DIII-D tokamak, the injection of deuterium pellets is being investigated as a means of controlling the toroidal rotation velocity and the radial electric field, Er. Solid deuterium cylindrical pellets of 1.8mm and 2.7mm diameter have been injected into single null diverted plasmas at 1.0 MA and 2.1T. Plasmas with either upper null or lower null diverted configurations were studied. The pellets have been injected from a number of locations including radial injection from the plasma outer midplane, vertically inside the magnetic axis, and from two locations on the inner wall. The penetration of the pellets is as deep as the axis for inner wall injection and to ρ=0.4 with radial outside midplane and vertical injection. The pellets significantly perturb the electron density profiles and initial results indicate a decrease in the toroidal rotation velocity such that toroidal angular momentum is conserved. From a radial force balance analysis it is seen that the injected pellets can significantly affect the radial profile of Er.